1. Field of the Invention
This invention concerns an endplay adjustment system and method for reducing or eliminating endplay associated with an armature of electric motor.
2. Description of the Related Art
FIG. 11 illustrates a prior art endplay adjustment system 100 used in an electric motor (not shown) having an armature (not shown) that drives a driven gear. The system 100 has a plunger 102 that is attached to a slider body 104 having an angled face 105 with attachment fingers 106. The plunger 102 comprises a plurality of interlocking ribs 108 that cooperate and lock against ribs 110 that are situated on the slider body walls 104a and 104b in order to lock the plunger 102 to the slider body 104.
The angled face 105 engages an end of the armature (not shown) when the system 100 is inserted in the motor. Due to angled face 105 of the slider body 104, there are large variations of stall torque between thrusting between the armature and the motor case side. This is caused by the angled face 105 side loading the armature shaft. This also increases friction in one thrust direction and a change in the worm angle in relation to a gear due to the flexure of the armature shaft. The stall torque variation is an undesirable trait for a bi-directional motor.
The angled face 105 also creates a high bending stress on the armature shaft of the electric motor when the motor stalls and the shaft thrusts against the angled face 105. This high stress requires that higher strength be used and stress-reducing features be added to the shaft geometry which impacts the cost of the armature shaft.
Moreover, the interlocking ribs 108 and 110 allow for an adjustment precision of approximately 0.15 mm and this is difficult to improve because it would require making the interlocking ribs 108 and 110 smaller. The interlocking ribs 108 and 110 must be made of a “soft” or flexible polymer to permit the interlocking ribs 108 and 110 to flex.
It has been found that the level of motor noise “growl” has been shown to correlate to an amount of axial force that is applied to the armature shaft as a result of the endplay adjustment process. The level of motor “clunk” noise correlates to the amount of gap that is allowed between the armature shaft and the endplay device. Due to the variation in friction between the plunger, slider body and gear housing walls, controlling the resulting axial force, while ensuring that there is no gap between the shaft and endplay device, is has been difficult. To ensure a maximum endplay gap is taken up, high forces are required to exert on the plunger top 112 downward (as viewed in FIG. 11) in order to engage the locking ribs 108 and 110.
One prior art design utilized a plunger 102 that was attached to the slider body 104 by the two attachment fingers (one of which is shown and labeled as 106 in FIG. 11). At times, the plunger 102 became tilted, relative to the slider body 104, the plunger will not engage the slider body 104 properly, thereby delaying or preventing the installation of the endplay adjustment system into the motor housing.
What is needed therefore is an endplay adjustment system and method which overcomes one or more of the problems associated with the prior art.